Abstract
At present, Sn-3.0Ag-0.5Cu (SAC305) solder is one of the commonly used lead-free solders, and copper-clad laminate is the commonly used PCB substrate. SAC solder and copper substrate mainly generate two intermetallic compounds (IMCs) of Cu6Sn5 and Cu3Sn during the soldering process. Based on the first principles, this paper analyzes the formation difficulty of the two kinds of IMCs generated in the soldering, and the failure mechanism of the Sn/IMC and IMC/Cu interfaces. Firstly, based on the density functional theory (DFT), the “CASTEP” module in Material Studio (MS) is used to analyze the formation difficulty of the two IMCs from the point of the density of states, population analysis, and energy. The results show that Cu6Sn5 is easier to generate, which also explains the reason for the first generation of Cu6Sn5 in the initial stage of soldering. Then, Sn / IMC and IMC / Cu interfaces were established in MS, and the reason why solder joint failure mainly occurred at the Sn / IMC interface was explained by energy analysis.
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